You need fibre, you need your magnesium, you need nutrients from veggies. Can you start drinking a veggie blend drink like v8 for starters? Think of salads with tomatoes, cucumbers, etc. for lunch or to go with dinner.
Toast or an egg for breakfast isn't enough. If you get your diet in order, then I'm sure that it will help with your energy and feeling weak.
Speak with your doctor and maybe talk with a nutritionist too if you want to look at what you're eating.